OrderManager.cs

/// all required usings

public sealed class OrderManager: IOrderManager 
{
    private IOrderValidator _validator;
    private IDeliveryManager _deliveryManager;
    private IRateExchange _rateExchange;
    private IAccountManager _accountManager;
    private IProductManager _productManager;
    private IEmailService _emailService;
    
    public OrderManager(
       IOrderValidator validator,
       IDeliveryManager deliveryManager,
       IRateExchange rateExchange,
       IAccountManager accountManager,
       IProductManager productManager,
       IEmailService emailService)
    {
        _validator = validator;
        _deliveryManager = deliveryManager;
        _rateExchange = rateExchange;
        _accountManager = accountManager;
        _productManager = productManager;
        _emailService = emailService;
    }
    
    public void ProcessOrder(Order order) 
    {
        if (!validator.Validate(order)) 
        {
            throw new Exception("Order is invalid");
        }
    
        var user = _accountManager.GetUserById(order.UserId);
    
        var mailToUser = GenerateMailMessage(order, user);
        _emailService.Send(mailToUser);
    
        if (order.IsDeliverable) 
        {
            _deliveryManager.Deliver(order, user);
        }
    }
    
    private MailMessage GenerateMailMessage(Order order, User user) 
    {
        var mailBodyBuilder = new StringBuilder();
        mailBodyBuilder.AppendLine($"Hello, {user.Name}!");
	
        var rate = _rateExchange.GetRate(user.Currency);
		    var dbProducts = order.Products.Select(orderProduct => _productManager.GetProduct(orderProduct.Id));
		    mailBodyBuilder.AppendLine(GetProductsText(dbProducts, rate));
        
        return new MailMessage(
            _emailService.ShopEmail,
            user.Email,
            "Thank you for your order!",
            mailBodyBuilder.ToString());
    }
    
    private string GetProductsText(IEnumerable<Product> products, double rate)
    {
    	// Something processing
    }
}